I have had the exact same issue with NEMA dropping out of my Ifly 720 trying to feed my GRT EFIS. It becomes so troublesome that now I no longer even use the Ifly to support the EFIS. The ifly is now used as a moving map only. It is a shame because this 720 is a great little unit.
I do have one question for the Ifly tech people my 720 is extremely slow booting up when I turn it on over 2 1/2 minutes is the 740 be faster?